Stripline resonator measurements of Zs versus Hrf in YBa2Cu3O7-x thin films

A report is presented on measurements of the surface impedance, Z_S, of YBa₂Cu₃O_7-x thin films using a stripline resonator. The films were deposited on LaAlO₃ substrates by off-axis magnetron sputtering. The authors obtained Z_S as a function of frequency from 1.5 to 20 GHz, as a function of temperature from 4 K to the transition temperature (~90 K), and as a function of the RF magnetic field from zero to 300 Oe. At low temperatures the surface resistance, R _S, of the films shows a very weak dependence on the magnetic field up to 225 to 250 Oe. At 77 K, R_S is proportional to the square of the field. The penetration depth shows a much weaker dependence on the field than does R_S. The origins of the magnetic field dependence of Z_S are also discussed     

Microwave shielding effectiveness of EC-coated dielectric slabs

Correct formulas for the microwave shielding effectiveness (SE ) of a thin metallic layer deposited on top of a dielectric slab are derived. For coatings much thinner than the skin depth, the following holds: (a) in a half-wave geometry, SE is a function of a sheet resistance only, SE (in dB)=20×log(1+188.5/R_s) if R_s is in ohms per square; (b) in a quarter-wave geometry, SE (in dB)=20×log[(1+ε_r)/(2√ε _r)+188.5/(√ε_rR_s)], where ε_r refers to the dielectric constant of the substrate. These formulas provide upper and lower limits for the effective shielding performance of an electroconductive coated dielectric slab     

The effects of source/drain resistance on deep submicrometer deviceperformance

As MOSFET channel lengths approach the deep-submicrometer regime, performance degradation due to parasitic source/drain resistance (R _sd) becomes an important factor to consider in device scaling. The effects of R_sd on the device performance of deep-submicrometer non-LDD (lightly doped drain) n-channel MOSFETs are examined. Reduction in the measured saturation drain current (R_sd=600 Ω-μm) relative to the ideal saturation current (R_sd=0.0 Ω-μm) is about 4% for L_eff=0.7 μm and T_ox =15.6 nm and 10% for L_eff=0.3 μm and T _ox=8.6 nm. Reduction of current in the linear regime and reduction of the simulated ring oscillator speed are both about three times higher. The effect of salicide technologies on device performance is discussed. Projections are made of the ultimate achievable performance     

Super low-noise HEMTs with a T-shaped WSix gate

A T-shaped quarter-micron gate structure composed of WSi_x /Ti/Pt/Au has been developed for low-noise AlGaAs/GaAs HEMTs. The gate resistance R_g was reduced to 0.3 Ω for devices with 200 μm-wide gates despite using WSi_x, and the source resistance R_s reached 0.28 Ω mm by minimising the source-gate distance using a self-alignment technique. This HEMT exhibited the lowest reported noise figure of 0.54 dB with an associated gain of 12.1 dB at 12 GHz     

Microwave measurement of temperature and current dependences ofsurface impedance for high-Tc superconductors

Perturbation formulas for TE₀₁₁-mode dielectric rod resonator and for a TE₀₁₁-mode circular cavity resonator are derived to determine the surface impedance Z_s of superconductors from measured values of resonant frequencies and unloaded Q. The relation between the maximum surface current density of a superconductor, J_s, and output power from a signal generator is derived. On the basis of these analytical results, a measurement technique is proposed to evaluate the temperature and J_s dependencies of Z_s for superconductors. The measured results of the temperature dependence of Z_s for YBCO and copper plates are presented. From these results, it is verified that the dielectric resonator is suitable for measuring the surface reactance for YBCO. From these Z_s values the temperature dependences of the skin depth and the penetration depth and those of the complex conductivity are obtained on the basis of the two-fluid model. These measured values agree well with the theoretical curves     

Thermal behavior of visible AlGaInP-GaInP ridge laser diodes

The thermal behavior of visible AlGaInP-GaInP ridge laser diodes was investigated numerically and experimentally. It is shown that various parameters critically influence the thermal resistance, R , of such devices. R is inversely proportional to the thermal conductivity of the heat sink. A substantial improvement in R is achieved for junction-side-down mounting compared to junction-side-up. R depends strongly on the width, w, of the ridge, and this effect is different for junction-side-up or junction-side-down mounting. In the first case, R~log(w) and in the second, R~1/w. The thickness of the soldering material is a sensitive parameter which may increase the value of R by up to 15 K/W. For junction-side-up mounted devices, the top metallization layer has a very favorable effect: a 1-μm-thick gold layer reduces R by 30%. It is shown that when a laser is switched on, the thermal steady state is reached in the millisecond time range. The experimental results show very good agreement with numerical data     

Measured performance at 77 K of superconducting microstripresonators and filters

Results on three types of passive microwave devices fabricated and tested using epitaxial thin films of Tl₂CaBa₂Cu ₂O₈ grown on LaAlO₃ are reported. A microstrip ring resonator with unloaded Q of 2740 at 77 K and 33 GHz is described. A superconducting 4.6 GHz band-reject filter with unloaded Q greater than 15000 when operated at 77 K is reported. In addition, results on a multiple microstrip bandpass filter are presented     

Measurement of collector and emitter resistances in bipolartransistors

New DC methods to measure the collector resistance R_C and emitter resistance R_E are presented. These methods are based on monitoring the substrate current of the parasitic vertical p-n-p transistor linked with the n-p-n intrinsic transistor. The p-n-p transistor is operated with either the bottom substrate-collector or the top base-collector p-n junction forward-biased. This allows for a separation of the various components of R_C. R_E is obtained from the measured lateral portion of R_C and the collector-emitter saturation voltage. Examples of measurements on advanced self-aligned transistors with polysilicon contacts are shown. The results show a very strong dependence of R_C on the base-emitter and base-collector voltages of the n-p-n transistor. The bias dependence of R_C is due to the conductivity modulation of the epitaxial collector. From the measured emitter resistance R_E a value for the specific contact resistance for the polysilicon emitter contact of ρ_c≅50 Ω-μm² is obtained     

Influence of free carrier plasma effect on carrier-inducedrefractive index change for quantum-well lasers

The influence of the free carrier component due to the plasma effect on carrier-induced refractive index change and its dependency on polarization for multiple-quantum-well (MQW) and bulk lasers are experimentally studied. The ratios of the component to the total index change, R_fc, are 0.6, 0.4, and 0.1 for 1.3-μm MQW, 1.3-μm bulk, and 0.8-μm MQW lasers, respectively. The TM/TE polarization ratios of the component, R_TMTE/, are 0.8 and 0.3 for 1.3-μm MQW and 0.8-μm MQW lasers. The relationship between the index change and the carrier overflow (to barrier and separate confinement heterostructure layers) for MQW lasers is also discussed. Large R_fc and R_TMTE/ for the 1.3-μm MQW laser result from the carrier overflow     

Design and experimental characteristics of strained In0.52Al0.48As/InxGa1-xAs (x>0.53)HEMTs

Strained In_0.52Al_0.48 As/In_xGa _1-xAs (x>0.53) HEMTs (high electron mobility transistors) are studied theoretically and experimentally. A device design procedure is reported that is based on band structure and charge control self-consistent calculations. It predicts the sheet carrier density and electron confinement as a function of doping and thickness of layers. The DC performance at 300 K is presented. Wafer statistics demonstrate improvement of device characteristics with excess indium in the channel (g¯_{m, intr}=500 and 700 mS/mm for x=0.60 and 0.65). Microwave characterization shows the f_T improvement (f_T=40 and 45 GHz for x=0.60 and 0.65, respectively) and the R_ds limitations of the 1-μm-long-gate HEMTs     

Noise performance at cryogenic temperatures at AlGaAs/InGaAs HEMT'swith 0.15-μm T-shaped WSix gates

T-shaped 0.15-μm WSi_x gate HEMTs have been fabricated on AlGaAs/InGaAs MBE wafers. Their S-parameters, output noise spectral density P_no, and noise temperatures T _e at cryogenic temperatures, were measured. The current gain cutoff frequency f_T increases from 61 GHz at 295 K to 87 GHz at 90 K. P_no and T_e measurements indicate that the hot-electron effect is noticeable at low temperatures at high drain current. At 30 GHz, the noise temperature is 19±3 K with an associated gain of 10.4 dB at the physical temperature of 20 K. The results demonstrate the great potential of AlGaAs/InGaAs HEMTs for low-temperature applications     

High-temperature superconductor resonators and phase shifters

High-T_c resonators and hybrid digital phase shifters have been designed, fabricated, and tested. The YBa₂Cu₃O_7-δ (YBCO) films used were off-axis sputtered onto 0.5-mm-thick [100] LaAlO₃ substrates and have surface impedances at 10 GHz as low as 20 μΩ at 4.2 K and 300 μΩ at 77 K. The dielectric constant of the LaAlO₃ substrates was measured using straight-line and ring resonator techniques. The superconductor straight-line resonator, which uses silver as its ground plane, has a moderately high Q factor and has an electromagnetic feedthrough level below -65 dB up to 10 GHz. The authors also report the first demonstration of a semiconductor/superconductor microwave digital phase shifter. YBCO film was used to form the circuit, with semiconductor p-i-n diodes serving as switches. A 4-b superconductor phase-shifter design is also presented along with simulation results that indicate maximum total insertion loss (which occurs with all bits forward-biased) at 77 K to be 1.1 dB at 10 GHz     

Input filter design criteria for switching regulators usingcurrent-mode programming

Design criteria are developed for a constant-frequency current-programmed switching DC-to-DC converter with an input filter to ensure stability and prevent performance degradation. The criteria are given in terms of the filter voltage transfer function H_S , output admittance Y_s, and the y-parameter model of the switching converter. The criteria are listed as four inequalities and illustrated graphically. The criteria may be summarized as follows: assuming a converter that satisfies its loop gain T, line-to-output transfer function A_gf , and output impedance Z_of requirement is given, an input filter with H_s and Y_s can be used to attenuate the noise emissions from the converter without adversely affecting the converter if H_s⩽1 (may be relaxed to 3-6 dB), and Y _s is larger than the curves of the graphical illustration, perhaps using 6 dB as a rule-of-thumb minimum separation     

Optimized trench MOSFET technologies for power devices

Low-voltage silicon trench power MOSFETs with forward conductivities approaching the silicon limit are reported. Vertical trench power MOSFETs with the measured performances of V_DB =55 V (R_sp=0.2 mΩ-cm², k _D=5.7 Ω-pF) and V_DB=35 V (R_sp=0.15 mΩ-cm², k_D =4.3 Ω-PF) were developed where V_DB is the drain-source avalanche breakdown voltage, R_sp is the specific on-state resistance, and k_D=R _spC_sp is the input device technology factor where C_sp is the specific MOS gate input capacitance. The optimum device performance resulted from an advanced trench processing technology that included (1) an improved RIE process to define scaled vertical silicon trenches, (2) silicon trench sidewall cleaning to reduce the surface damage, and (3) a novel polysilicon gate planarization technique using a sequential oxidation/oxide etchback, process. The measured performances are shown to be in excellent agreement with the two-dimensional device simulations and the calculated results obtained from an analytical model     

p-channel FET based on p/n double-quantum-well heterostructure

An experimental demonstration of a p-channel FET based on a heterostructure having vertically integrated p- and n-type quantum-well channels is discussed. The AlGaAs/GaAs heterostructure consists of a quantum well with an underlying p-region positioned above a second quantum well with an underlying n-region. The p-FET is fabricated with self-aligned p⁺ regions formed by zinc diffusion. Electrical characteristics for 1.5-μm gate lengths are nearly ideal in appearance with a maximum I_d of 90 mA/mm, a g _m of 80 mS/mm, and a g_m/g _d ratio of 140 at 77 K. The results demonstrate the viability of such stratified structures for the development of complementary integrated circuits or other circuits requiring integration of multiple device types     

Statistical inference under multiterminal rate restrictions: adifferential geometric approach

A statistical inference problem for a two-terminal information source emitting mutually correlated signals X and Y is treated. Let sequences Xⁿ and Yⁿ of n independent observations be encoded independently of each other into message sets M_X and M_Y at rates R₁ and R ₂ per letter, respectively. This compression causes a loss of the statistical information available for testing hypotheses concerning X and Y. The loss of statistical information is evaluated as a function of the amounts R₁ and R ₂ of the Shannon information. A complete solution is given in the case of asymptotically complete data compression, R₁, R₂→0 as n→∞. It is shown that the differential geometry of the manifold of all probability distributions plays a fundamental role in this type of multiterminal problem connecting Shannon information and statistical information. A brief introduction to the dually coupled e-affine and m-affine connections together with e -flatness and m-flatness is given     

On the low-temperature static and dynamic properties ofhigh-performance silicon bipolar transistors

In a study performed over the temperature range of 400 to 77 K, Si bipolar transistors were found to have near-ideal characteristics at low temperatures with β as high as 80 at 77 K. Detailed calculations indicate that the conventional theory of the temperature dependence of β does not match the data. The discrepancy can be removed if it is assumed that a phenomenological thermal barrier to hole injection is present. Emitter-coupled logic (ECL) ring oscillators are functional at 85 K with no degradation in speed until about 165 K when compared to 358 K (85°C). Calculations using a delay figure of merit indicate that f_T, R_b, and C_c are the delay components most affected by low-temperature operation. The feasibility of reduced logic swing operation of bipolar circuits at low temperatures is examined. It is found that successful ECL circuit operation at reduced logic swings is possible provided emitter resistance is kept small and can be used to enhance low-temperature power-delay performance. These data suggest that conventionally designed high-performance bipolar devices are suitable for the low-temperature environment     

Roles of low field mobility and its carrier-concentrationdependences in high electron mobility transistors and other field effecttransistors

A model is proposed for high-electron-mobility transistors (HEMTs) and other heterostructure FETs in which the dependence of low field mobility μ on carrier concentration N_s is taken into account. On the basis of this model, the influence of μ and its N_s dependence on drain current and transconductance g_m are clarified, In particular, high mobility (>10⁵ cm²/V-s) is shown to be effective in achieving and maintaining the intrinsic limit of g_m(=ε₂ν_s/d*) irrespective of bias conditions, where ν_s is the saturation velocity and ε₂ and d* are the dielectric permittivity and the effective thickness of the gate insulator, respectively. The N_s dependence of mobility is found to greatly affect the gate-voltage dependence of g _m and leads, in some cases, to an appreciable increase of g_m above its intrinsic limit     

GaAs/AlGaAs quantum-well, long-wavelength infra-red (LWIR) detectorwith a detectivity comparable to HgCdTe

The authors achieved the first high responsitivity R_v=30000 V/W, high detectivity D*=1×10¹⁰ cm √(Hz)/W GaAs/AlGaAs multiquantum-well superlattice detector which is sensitive in the long wavelength infra-red (LWIR) spectral region. This detector operates at λ=8.3 μm and at a temperature of T=77 K     

Gain anisotropy and simultaneous bidirectional emission of aDoppler-broadened MIR optically-pumped ammonia ring laser

The authors studied the Doppler-broadened 11.76-μm ¹⁵NH₃ emission line optically pumped in a ring resonator by a CW CO₂ laser operating on the 10R(42) line. Behavior related to the optical pumping of gas Doppler-broadened lines is found and shown to be very dependent on the laser parameters. For instance, the laser emission can occur in one direction or two directions simultaneously. A local gain model based on the interaction of two laser fields with a three-level molecular system is used to clarify the emission characteristics of this laser. Basically, the two-photon or Raman process and the Rabi splitting generate a gain anisotropy and an anomalous dispersion curve. The effects lead to a different optical path for the two directions of propagation and, consequently, a simultaneous bidirectional emission with unequal emission frequency